Importance of Rodent Control in Biosecurity Programs

A growing number of poultry and egg producers in North America have
learned to appreciate how a biosecurity program can reduce the
potential for disease transmission and contribute to their overall
profitability.

A growing number of poultry and egg producers in North America have
learned to appreciate how a biosecurity program can reduce the
potential for disease transmission and contribute to their overall
profitability.  Given the threat of highly pathogenic avian influenza and public concern, an effective biosecurity program is now more important than ever.  However, producers with biosecurity programs in place may have overlooked the importance of rodent control in a successful biosecurity program.

Breaking the cycle
The U.S. Poultry & Egg Association (PEA) defines biosecurity as “a health plan to prevent the occurrence and transmission of infectious diseases.”  Infection of poultry populations is essentially a cycle.   If the cycle is broken – even by reducing or removing one element – the risk of infection drops significantly.

At any individual poultry operation, there are several key control points where the entry or transmission of pathogens can be prevented. These include:
•    Entrance to the farm
•    Entrance to the poultry houses
•    Cross-contamination in brooding and growing
•    Bird disposal
•    Litter management and disposal
•    Farm sanitation
•    Pest control

Among poultry facility pests, rodents are a major source and spreader of infections, crossing site boundaries and taking up residence in and around breeder, broiler and layer houses.  The presence of rodents also stresses flocks, potentially making them more susceptible to disease. The PEA identifies rodent infestation as a major biosecurity risk factor and recommends that producers seek immediate professional assistance in controlling an existing infestation and preventing future infestations.

Comprehensive approach
Biosecurity is a common-sense process.  Producers of any size can establish a comprehensive program consisting of simple steps tailored to their specific type and size of operation.  An effective biosecurity program requires a look at every facet of the operation with an eye toward minimizing the risk of disease pathogen entry and transmission.  It depends mainly on strictly enforced procedures and preventive measures that every employee can easily follow.  However, the program must not be overly restrictive and cumbersome and must be consistent with high productivity and profit. The PEA has introduced five steps that producers can follow to develop a biosecurity program tailored to their needs:

Assess risks. Make a list of conditions present on the farm, such as a rodent infestation, which may increase the probability of disease. Define needed biosecurity measures. Make a “to-do list” of things you must do to correct the conditions causing the risks.  Consider the relative cost-benefit of each one.

Implement the measures. Put all the necessary controls into practice.  Include training in the “why and how” for all employees.  Make sure procedures are enforced consistently.
Monitor risks and progress. Perform regular check-ups to make sure the program is being followed.  Be alert for new risk factors that may result from changes in the production environment or in local disease conditions.

Adjust as necessary. Make changes as conditions change. Involve all key players, including farm employees and technical services staff.

Two phases
An effective biosecurity program must have two phases to match the production phases of the facility: “Cleanout Disinfection” and “Re-infection Prevention.”

Phase 1 – Cleanout disinfection
•    Cleanout disinfection takes place after a facility has been cleared to prepare the way for a new flock. Its fundamental components include:
•    Removing as much filth, feed and manure as possible
•    Cleaning and disinfecting the water and feed systems
•    Cleaning and disinfecting equipment and vehicles
•    Cleaning and disinfecting the structure
•    Eliminating insect infestations
•    Eliminating rodent infestations

A key element of the cleanout disinfection is an “intensive rodent control treatment.”
As soon as the birds have been removed eliminate as much feed as possible.

For house mice, place a fast-acting rodenticide with bromethalin as the active ingredient, in trays eight to 12 feet apart around the interior perimeter of the building.  Maintain an uninterrupted supply of bait.  Move material from areas with no activity to areas with high activity.  As feeding subsides, switch to a rodenticide with high palatability. Use it as a “clean-up hitter” to eliminate any mice which did not feed on the bromethalin bait. 

Do not use rodenticide pellets for mouse control.  Mice tend to translocate them and cache them, thereby creating the risk they may be accessible to chickens later.

For roof rats, which are by nature a tropical tree dweller, use a rodenticide formulated with flavourings attractive to this species, such as Hombre.  Place it in their runways, which are usually above the floor.  Use wire, nails and bait stations to secure the material.

For Norway rats, which are ground burrowing rodents, the most effective treatments are applications of loose pellets directly into their burrow.  Blocks placed in burrows often trigger a “fear of new object” reaction causing the rat to kick them out rather than feed on them.  Pellets that are parafanizzed to withstand the moist environment of the burrow resemble seeds blown in by the wind and are readily accepted.

Re-treat all burrows at least weekly until all signs of activity cease.  Do not cave burrows in after treatment so pellets are not expelled when the rat reopens the burrow.

Phase 2 – Re-infection prevention
Re-infection Prevention maintains biosecurity throughout the process of raising the new flock.  Because anyone or anything that enters a facility may carry disease, access needs to be controlled by measures such as:
•    Visitor restrictions
•    Clean or disposable clothing – coveralls and boots
•    Vehicle restrictions and disinfection
•    Hand and footwear cleaning and sanitizing
•    Preventive insect control
•    Preventive rodent control
A critical part of re-infection prevention is the establishment of a “preventive rodent control” program:

First, eliminate as many food and harborage sources around buildings to make the area less attractive to rodents.  Remove weeds, bushes, litter heaps, animal carcasses, feed spills, old equipment and debris.  Keep grass mowed.  Consider a crushed rock perimeter past the roof drip line around the building to deny rodents, especially mice, a breeding place in grass next to the building.

The next step in preventive rodent control is exclusion. Reduce the likelihood of rodent entry by repairing holes in the structure, securing loose ventilation grills and making sure doors fit well on the sides and at the bottom.

Then, position tamper resistant rodenticide bait stations strategically to intercept rodents approaching the facility from surrounding environments. Stock them with a rodenticide formulated for high palatability so rodents are likely to feed on it as soon as they encounter it.  Put enough rodenticide in each bait station to assure an uninterrupted supply from one service to the next.

Finally, place traps and rodenticides inside buildings to quickly eliminate any rodents that make it past the exterior defenses.  Whenever rodents are noticed, take aggressive action to eliminate them before they become established.

Rotating rodenticides
In modern rodent control the most commonly used rodenticides are anticoagulants.  These materials inhibit blood clotting, causing internal bleeding and a painless death for the rodent within several days.   This relatively slow action does not trigger bait shyness, which is common with fast-acting (acute) rodenticides.  All anticoagulant rodenticides share a common, readily available antidote in vitamin K-1.  None of the acute rodenticides have an antidote.  The anticoagulant rodenticides also work at lower concentrations of active ingredient than the acute toxicants so they are more readily accepted and fed on by rodents.
The concept of rodenticide rotation began in the 1970s as mice and rats developed metabolic resistance to warfarin, which is a multiple feed anticoagulant rodenticide.  Due to an inherited biological trait, resistant rodents were able to eat and metabolize many times more than what should have been a lethal dose.  To counter this resistance, pest managers turned to non-anticoagulants and new single-feed anticoagulants.

To our knowledge, there is no known metabolic resistance to any of the modern anticoagulant rodenticides used in North America.  Still, rotation remains an appropriate strategy because rodents may have a tendency to avoid a particular rodenticide flavour, texture or shape.  Also, the future development of metabolic resistance is possible if one active ingredient is used exclusively.

A simple and effective rotation program will start with a single-feed anticoagulant rodenticide containing difethialone.  After six months, switch to a product containing a different single feed anticoagulant, such as bromadiolone in a different mixture of food ingredients, for the next six months.  During cleanout, use a product containing the acute toxicant bromethalin.

Some growers prefer a rotation with shorter cycles and without an acute toxicant, such as four months difethialone then two months bromadiolone then back to difethialone etc.  The cycle is not as important as actually starting and then sticking with a rotation plan, which is practical for the individual grower using it.

Breeding success
In recent years, the poultry and egg industry has raised itself to unprecedented levels of professionalism and success.  However, outbreaks of disease threaten public confidence and the strength of the industry.

A sound biosecurity program is a necessary and affordable form of insurance to protect all that the industry has achieved. That protection must include effective rodent control as one of the most critical safeguards.  

Claude Thibault, DVM, is Manager, Technical Services, Vétoquinol Canada Inc.   Ted Bruesch is National Technical Support Manager, Liphatech Inc.